Cell - Identification of Candidate IgG Biomarkers for Alzheimer's Disease via Combinatorial Library Screening

Identification of Candidate IgG Biomarkers for Alzheimer's Disease via Combinatorial Library Screening

Cell, Volume 144, Issue 1, 132-142, 7 January 2011
Copyright © 2011 Elsevier Inc. All rights reserved.
10.1016/j.cell.2010.11.054

Referred to by: Fishing for Biomarkers with Antigen Mimi...
Authors
M. Muralidhar Reddy, Rosemary Wilson, Johnnie Wilson, Steven Connell, Anne Gocke, Linda Hynan, Dwight German, Thomas Kodadeksend emailSee Affiliations

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Opko Health Laboratories, 130 Scripps Way, Jupiter, FL 33458, USA Departments of Chemistry & Cancer Biology, The Scripps Research Institute, Scripps Florida, 130 Scripps Way, #3A2, Jupiter, FL 33458, USA Division of Translational Research, Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA Department of Clinical Sciences, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA Department of Psychiatry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA Corresponding author

Summary

The adaptive immune system is thought to be a rich source of protein biomarkers, but diagnostically useful antibodies remain unknown for a large number of diseases. This is, in part, because the antigens that trigger an immune response in many diseases remain unknown. We present here a general and unbiased approach to the identification of diagnostically useful antibodies that avoids the requirement for antigen identification. This method involves the comparative screening of combinatorial libraries of unnatural, synthetic molecules against serum samples obtained from cases and controls. Molecules that retain far more IgG antibodies from the case samples than the controls are identified and subsequently tested as capture agents for diagnostically useful antibodies. The utility of this method is demonstrated using a mouse model for multiple sclerosis and via the identification of two candidate IgG biomarkers for Alzheimer's disease.

* There is great interest in the discovery of disease-specific protein biomarkers in easily accessible biological fluids such as serum. A particularly interesting subproteome in this regard is the IgG antibody population (Anderson and LaBaer, 2005). The adaptive immune system is known to react specifically to many different disease states, in part through the amplification of particular antibodies that recognize disease-specific antigens. Thus, it should be possible to devise diagnostic tests for many different diseases based on the measurement of the levels of these antibodies in serum. However, this has proven difficult. Because antibodies are highly specific receptors for their cognate antigens, the general thinking is that a diagnostic test designed to monitor the level of a disease-specific antibody would require immobilized antigen as a “capture agent.” Unfortunately, there are many pathogenic conditions, including autoimmune diseases, neurological conditions, and cancers, for which the antigens that trigger the primary immune response are unknown, and thus, a definitive blood test is not available.

* To address this problem powerful proteomics technologies have been employed to screen large collections of expressed proteins, peptides, or other biomolecules in an attempt to discover native antigens recognized by disease-specific antibodies. Some notable successes have been achieved (Fathman et al., 2005,Frulloni et al., 2009,Gibson et al., 2010,Hudson et al., 2007,Kanter et al., 2006,Lueking et al., 2003,Robinson et al., 2002b,Steller et al., 2005,Wang et al., 2005). However, none of these techniques appears to represent a general route to the rapid discovery of antibody biomarkers of real diagnostic utility. It is reasonable to suspect that a limitation of screens that employ collections of unmodified peptides, proteins, or lipids is that they are unlikely to contain the primary autoantigens that trigger the earliest and most disease-specific autoimmune response. It seems more likely that these primary antigens are biomolecules that are chemically modified in unusual ways due to the pathogenic chemistry involved in that particular disease state. In other words, it may be that collections of unmodified biomolecules represent the wrong region of “chemical space” in which to be looking for autoantigens or mimics thereof.

* With this hypothesis in mind, we were interested in testing a fundamentally different approach in which a combinatorial library of unnatural synthetic molecules is screened for ligands that bind antibodies abundant in the serum of animals or patients with a particular disease, but not healthy controls. The idea behind this approach is that unnatural molecules will simply represent a “shape library” that occupies regions of chemical space outside of that represented by unmodified biomolecules. A few of these molecules might, by chance, recognize the antigen-binding pocket of disease-specific antibodies well enough to retain them from the blood, though they would almost certainly not bind as well as the (unknown) native antigens. This is the thinking behind almost any high-throughput screen of synthetic molecule libraries or collections against protein drug targets of pharmaceutical interest. Moreover, whereas antibodies are generally not considered drug targets, it is known that antibody ligands with structures quite different from that of the native antigen can be isolated through library screening. For example, peptide libraries have been screened successfully for “mimotopes” that bind to carbohydrate-binding antibodies, and these peptides can even be used as vaccines to raise antibodies against the native carbohydrate antigen (Knittelfelder et al., 2009). However, to the best of our knowledge, all such mimotope screens have employed a single, well-defined antibody target and have not been utilized in de novo searches for diagnostically useful antibody biomarkers.

* We demonstrate here that microarrays displaying thousands of peptoids (N-substituted oligoglycines; Simon et al., 1992) can be used along with a differential screening strategy for the simultaneous isolation of candidate IgG antibody biomarkers and selective peptoid ligands able to pull them out of the blood. In two mouse models it is shown that these peptoids are antigen surrogates in the sense that they bind selectively to the antibodies raised against the antigen employed to trigger the disease state. This methodology provides an unbiased approach to the discovery of IgG serum biomarkers that does not require prior knowledge of native antigens. In this report we describe the development of this technology and its application to a mouse model for multiple sclerosis. We also demonstrate that the approach is applicable to the discovery of potentially useful diagnostic biomarkers in humans through the discovery of compounds that bind antibodies that are present at high levels in the serum of patients with Alzheimer's disease (AD).
Cell - Identification of Candidate IgG Biomarkers for Alzheimer's Disease via Combinatorial Library Screening



NEUROLOGÍA
Actualidad Ultimas noticias - JANOes y agencias -
Un nuevo test sanguíneo podría detectar el Alzheimer

JANO.es y agencias · 10 Enero 2011 12:00

Esta prueba podría predecir la enfermedad mediante la búsqueda de anticuerpos en la sangre de los pacientes.

Un grupo de investigadores estadounidenses ha descubierto la forma de predecir la enfermedad de Alzheimer mediante la búsqueda de anticuerpos en análisis sanguíneos. Los resultados podrían conducir, según los autores, "al desarrollo de un test sanguíneo para detectar la enfermedad".

"El cuerpo produce anticuerpos en respuesta a la presencia de enfermedades. Nosotros queremos desarrollar test sanguíneos que nos permitan encontrarlos", explica el autor principal de la investigación, Thomas Kodadek.

El estudio, que se publica en Cell, ha utilizado moléculas creadas en laboratorio para evaluar la presencia de anticuerpos específicos de la enfermedad de Alzheimer. Los resultados indican que tres de estas moléculas han reaccionado en la sangre de seis pacientes afectados por la patología, mientras que se han mantenido neutras en pacientes sanos.

Asimismo, los científicos también aplicaron el test a 200 ancianos que no presentaban demencia y hallaron que un 8% de ellos presentaba concentraciones elevadas de los mismos anticuerpos encontrados en los pacientes con Alzheimer, lo que sugiere que la prueba podría servir para predecir la patología.

"Este sorprendente estudio tiene importantes implicaciones para avanzar en la compresión y tratamiento de diferentes demencias u otras enfermedades como la esclerosis múltiple", indica el investigador principal sobre enfermedades neurodegenerativas del Instituto Garvan de Sidney, Australia, Bryce Vissel.


Cell, Volume 144, Issue 1, 132-142, 7 January 2011
Cell - Identification of Candidate IgG Biomarkers for Alzheimer's Disease via Combinatorial Library Screening


Actualidad Ultimas noticias - JANOes y agencias - Un nuevo test sanguineo podria detectar el Alzheimer - JANO.es - ELSEVIER